The semiconductor industry has been known to divide a semiconductor wafer into a number of chips by scribing the wafer with a diamond saw scriber and pressing the wafer locally by a roller over the wafer to break the semiconductor wafer up into chips. This method, however, has numerous drawbacks, for example, scribing is limited to one direction and hence is very inefficient; a continuous scribing line is not available unless the wafer surface is smooth enough and the grooves formed are deep enough to divide the thick wafer. To solve these problems, a scribing apparatus using a laser beam has been proposed in which a laser beam of a given output level is applied directly to the semiconductor wafer, which is held on a stage by vacuum absorption, and the wafer is scribed or grooved by the laser beam as the wafer is moved. With this apparatus, the scribing speed is increased and the continuity of the scribed line is achieved. Moreover, the wafer is scribed deeply.
This prior art, however, using laser technology is disadvantageous in that molten semiconductor debris from the laser beam is scattered during the scribing and adheres to the chip surface on the wafer. The minute semiconductor debris that adheres to the electrodes or metal wiring on the chip will deteriorate the electrical properties of the chips, or ruin the function of the integrated circuit. When using mechanical sawing or scribing techniques chips or chipouts are caused by cracks that radiate away from the scribe in an active duct between the die into the active circuit, for example, the integrated circuit to be formed from the die, such that a portion of the silicon actually breaks out. The formation of these chipouts are facilitated by the structure of the silicon itself. The structure of the silicon is uniform such that the cracks follow the structure of the silicon until the crack has followed the structure of the silicon a sufficient distance which results in a piece of the silicon chipping out.
Even if these cracks do not travel along the structure of the silicon a sufficient distance to create a chipout of the silicon, these cracks can affect the operation of the integrated circuit device formed the die of the silicon. Thus, these cracks cause a defect with or without the chipout.
For example, if the crack extend into the die and does not cause a chip out, the crack remains in the bar during and after the assembly process. This may cause the die to actually crack after assembly inside the package, rendering the die useless.
These types of defects result in lost revenue when the cracked die is discovered before sale, and dissatisfied customers if the defect in the die is not discovered until after the purchase.
It has been recognized that hardening the silicon prevents some of these cracks from forming. This does not prevent all of the cracks from forming. Although these cracks may propogate in any direction. The cracks that propogate into the die cause the problems. The cracks that propogate along the path of the saw are generally less troublesome with respect to chipouts.
In order to protect the surface of the die, the die may be coated with a protection coating material, for example silicon nitride. If this protection coating is removed with the silicon during a chipout, this loss of protection coating may result in reliability of the integrated circuit is adversely affected. The removal of the protection layer expose the enter level oxides within the die and results the migration of sodium ionic contaminate, sodium being one possibility to the exterior of the die and then migrate along the interface of the inter-level oxide. This creates an inversion since the sodium enters the actual transistor.